Four-stroke internal combustion engines can be used in outdoor power tools, such as line-trimmers, edgers, chain saws, blowers, and the like. Four-stroke internal combustion engines can also be used for powering vehicles, such as motor cycles, all-terrain vehicles, and the like. Typical four-stroke internal combustion engines include a crankcase, a cylinder communicating with the crank case, and a piston adapted to reciprocate within the cylinder. During the combustion process, gases can flow past the piston rings and create elevated pressure in the crankcase.